1. Field of the Invention
The present invention relates to a LED and a lighting apparatus using the LED, and more particularly, to a lighting apparatus using the light emitting diode (LED) as a light source for an optical projection system.
2. Discussion of the Related Art
Generally, an optical projection system has employed a high pressure mercury lamp, a halogen lamp, a xenon lamp, etc., which emits light via an arc discharge, as a light source. However, the light source using the arc discharge has problems of high power consumption, requirement for high voltage and generation of heat during operation, and possibility of high pressure gas exploding. Furthermore, with such a light source, it is difficult to achieve highly pure colors due to a wide range of its light spectrum.
FIG. 1 is a plot depicting the spectrum of a light source of the optical projection system using the arc discharge. Here, the light source employs light of partial ranges corresponding to some parts of Red (R), Green (G), and Blue (B) ranges, respectively.
Referring to FIG. 1, among wavelength bands of R, G and B colors, the wavelength band of G color exhibits a great intensity of light, whereas the wavelength bands of B and R colors exhibit a small intensity of light. In particular, since B color has the lowest spectral sensitivity, the darkest color range is provided in the wavelength band of B color. In view of this, in order to realize a color image corresponding to an input image signal, a white balance must be obtained by reducing light intensity of green and red colors corresponding to the lowest light intensity of blue color. However, with the method as described above, only a part of the light from the lamp is used, and the light intensity of the particular colors must be reduced in order to achieve the white balance, thereby lowering utilization efficiency of light. In addition, it is difficult to exhibit pure and relatively natural colors since a wide range of wavelengths are used for emitting each color.
Accordingly, it has been suggested to employ a LED as a light source of low power and high efficiency. The LED is a device used to emit light according to an electrical signal, and generally used for small scale optical components and display devices as it can be driven with lower power. In particular, although the LED has not been used for a light source requiring high brightness, the LED has been continuously enhanced in light emitting efficiency, and thus found new applications for light sources requiring high brightness. Recently, the LED can be applied to the light source for the optical projection system, such as a projector, a projection TV, and the like.
However, due to feature of its configuration, it is difficult for the LED to provide parallel light or focused light which is required for the optical projection system as the light source. Furthermore, light is shielded by electrodes of the LED, and is emitted only in one direction. Accordingly, in order to employ the LED as the light source of the optical projection system, it is necessary to include an additional lens assembly which can provide optical characteristics required for the optical projection system.